title: Use of dMLC for implementation of dynamic respiratory-gated radiation therapy.
abstract: OBJECTIVE
  To simulate and evaluate the use of dynamic multileaf collimators (dMLC) in respiratory gating to compensate for baseline drift.
  
  
  METHODS
  Tumor motion tracking data from 30 lung tumors over 322 treatment fractions was analyzed with the finite state model. A dynamic respiratory gating window was established in real-time by determining the average positions during the previous two end-of-expiration breathing phases and centering the dMLC aperture on a weighted average of these positions. A simulated dMLC with physical motion constraints was used in dynamic gating treatment simulations. Fluence maps were created to provide a statistical description of radiation delivery for each fraction. Duty cycle was also calculated for each fraction.
  
  
  RESULTS
  The average duty cycle was 2.3% greater under dynamic gating conditions. Dynamic gating also showed higher fluences and less tumor obstruction. Additionally, dynamic gating required fewer beam toggles and each delivery period was longer on average than with static gating.
  
  
  CONCLUSIONS
  The use of dynamic gating showed better performance than static gating and the physical constraints of a dMLC were shown to not be an impediment to dynamic gating.
authors.affiliation: Purdue School of Engineering Technology, IUPUI, Indianapolis, Indiana 46202.
authors.forename: Eric W
authors.initials: EW
authors.lastname: Pepin
authors.forename: Huanmei
authors.initials: H
authors.lastname: Wu
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shirato
mesh_terms: D019583:Dose Fractionation, Radiation; D008175:Lung Neoplasms / Q000503:physiopathology* / Q000532:radiotherapy*; D008962:Models, Theoretical; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D012119:Respiration; D013997:Time Factors